Unlike certain rotary electric machines, rotary electric machines used in wind power turbines, particularly large wind power turbines, must have certain characteristics, such as relatively light weight, easy access for maintenance, and easy component part assembly, disassembly and transport, both at the first-assembly stage and when changing parts or making repairs. In addition, they must be connectable easily to the supporting frame and the blade assembly, and must be so designed as not to require excessively bulky, heavy supporting frames.
The tendency in the wind power turbine industry is towards increasingly high-power rotary electric machines, which makes it difficult to satisfy conflicting market demands.